Due to the residues of scarcely bleachable lignins, craft pulp as one of principal chemical pulps requires multi-stage bleaching in addition to the bleaching with chlorine chemicals. Because the liquid waste after such bleaching contains chlorine ions, therefore, it is difficult to recover the waste for treatment. Additionally, a report has been published recently that organic chlorine compounds including hazardous dioxines are contained in the liquid waste, which has been drawing attention as one of the sources for environmental pollution. Alternatively, the liquid waste after bleaching is severely colored and contains partially chlorinated lignin degradation products if activated sludge process, a well known process of liquid waste, is applied to the liquid waste. Thus, it is difficult to effectively treat the liquid waste with activated sludge process alone.
Therefore, attempts have been made for the treatment of the liquid waste after pulp bleaching via microorganisms, while focusing on a variety of microorganisms. For example, Japanese Patent Publication No. Hei 3-5878 describes a process of adsorbing or decomposing the chromaticity components in craft pulp liquid waste via the use of Penicillium janthinellum.
Disclosure has been made of examples for decoloring alkali lignins, humic acid and bile acid via the microorganism, but the process is not applied to the liquid waste of craft pulp bleaching so no demonstration of the decoloring effect on the liquid waste of craft pulp bleaching is made therein.
The decoloring of the liquid waste of craft pulp bleaching via Phanerochaete chrysosporium has been reported (Momohara et al., Lumber Research Society, 35(12), 1110(1989)), with the results that no decoloring occurs several days after such fungal treatment and that about two weeks are required for the fungal treatment so as to achieve satisfactory decoloring effect. Thus, the process has not been industrially applied in terms of the long period of treatment and less decoloring effect. Furthermore, a process of decoloring the liquid waste after lumber pulp bleaching has been proposed via Phanerochaete chrysosporium, using a porous carrier (Japanese Patent Laid-open No. Hei 1-503125), but the problem that the process also requires a long period of treatment time with less decoloring effect has remained unsolved.